Showing papers in "Physiological Entomology in 2006"

Chemically-mediated host-plant location and selection by root-feeding insects

Abstract: . Recent studies have shown that root-feeding insects can be of considerable importance in terms of agricultural damage, their indirect impacts on above-ground herbivores and their efficacy as biocontrol agents of weeds. To date, isolated studies have made it difficult to identify the mechanisms by which soil-dwelling insects locate and select host-plant roots. This review synthesizes 78 studies describing root location and selection. Soil insect herbivores do not rely on encountering roots at random, but orientate towards them using semiochemicals that enable specialist insects to distinguish host-plants from unsuitable plants. Secondary plant metabolites released into the rhizosphere (alcohols, esters and aldehydes representing 37% of reported examples) underpin host-plant location and recognition, with 80% having ‘attractant’ properties. Insects feeding on a limited range of plants tend to exploit host-specific secondary metabolites, whereas nonspecialist feeders appear to use more general semiochemicals. When insects reach the roots, contact chemosensory cues act as either ‘phagostimulants’ (48% of the compounds being sugars) or feeding ‘deterrents’ (notably phenolic compounds). Twenty studies conclude that CO2 is the major primary plant metabolite that allows insects to locate to roots. However, several features of CO2 emissions from roots mitigate against it as a precise location cue. In addition to its lack of specificity, gradients of root emitted CO2 do not persist for long periods and vertical gradients of CO2 in the soil tend to be stronger than horizontal gradients. A conceptual model is presented, emphasizing the importance of soil properties (e.g. porosity, moisture) on chemical diffusion and insect motility.

Cost and mitigation of insecticide resistance in the maize weevil, Sitophilus zeamais

Abstract: . A common assumption in models of insecticide resistance evolution is the association between resistance and fitness costs in the absence of insecticides. There is empirical evidence of such associations, but their physiological basis (and mitigation) is little investigated. Pyrethroid-resistant populations of the maize weevil Sitophilus zeamais (Coleoptera: Curculionidae) offer this opportunity. Pyrethroid resistance in this species was initially observed in five Brazilian states by 1995, but the phenomenon apparently decreased and did not spread to other regions, probably due to the occurrence of a fitness disadvantage in resistant individuals in the absence of insecticides. The present investigation aims to verify whether differences in respiration rate and fat body morphology are related to differences in rate of development in Brazilian populations of S. zeamais resistant to insecticides, and thereby provide evidence for the existence (or not) of a physiological fitness cost acting against insecticide resistance in maize weevils. This may occur due to a possible energy trade-off between insecticide resistance and other physiological processes associated with development and reproduction. To achieve this, studies of the rate of development, respiration and fat body cytomorphology are carried out in one insecticide-susceptible (from Sete Lagoas) and two resistant populations (from Jacarezinho and Juiz de Fora) of S. zeamais. The resistant population from Jacarezinho shows that higher body mass is associated with higher energy reserves (larger trophocyte area) for development and reproduction, as well as for insecticide resistance. However, the resistant population from Juiz de Fora does not appear to have large enough energy allocation for insecticide-resistance expression and development and/or reproductive performance, suggesting a trade-off between resistance and other life history traits.

The impact of fluctuating thermal regimes on the survival of a cold-exposed parasitic wasp, Aphidius colemani

Abstract: The impact of fluctuating thermal regimes on the cold tolerance of the parasitoid Aphidius colemani at the mummy stage is examined. The hypothesis is tested that, if a cold period is interrupted by a return to a higher temperature for a short time, a physiological recovery is possible and may lead to higher survival. Mummies are exposed to a constant temperature of 4 degrees C and, when periodic sudden transfers to 20 degrees C for 2 h are applied, survival of immature parasitoids is markedly improved, proportionally to the warming frequency. The time lag before emergence diminishes with the duration of cold exposure and with warming frequency. The sex ratio of emergent adults after cold exposure indicates that males may be more susceptible than females to cold-injury. It is suggested that the transfer to 20 degrees C allows a re-activation of the normal metabolism, leading to repair and recovery of any injuries caused by prolonged chilling. The study underlines the importance of cyclic temperature changes on insect survival.

Reorganization of membrane lipids during fast and slow cold hardening in Drosophila melanogaster

Abstract: Rapid cold hardening is a naturally occurring phenomenon in insects that is thought to be responsible for increased cold tolerance during diurnal variations in temperature. The underlying physiological mechanisms are still not fully resolved but, in Drosophila melanogaster (Meigen 1830), rapid cold hardening is accompanied by specific changes in the membrane lipid composition. To further understand the link between rapid cold hardening and adjustments in the membrane lipid composition, the present study investigates how different rates of cooling affect thermotolerance and the composition of phospholipid fatty acids. Female Drosophila are cooled gradually from 25 to 0 °C at 0.01, 0.05, 0.1 or 0.5 °C min−1, respectively, and, subsequently, phospholipid fatty acid composition and survival after a 1-h cold shock at −5 °C is measured. The rapid cold hardening treatments all influence cold tolerance differently so that short and intermediate rapid cold hardening treatments (0.05, 0.1 or 0.5 °C min−1 cooling rates) increase cold shock survival, whereas the slow cooling treatment (0.01 °C min−1) decreases survival relative to an untreated control. The intermediate rapid cold hardening treatments (0.05 or 0.1 °C min−1) induce a similar type of response characterized by an increase in the molar percentage of linoleic acid, 18:2(n-6), at the expense of 16:0 and 18:1(n-9), which leads to an increase in the degree of unsaturation. The slowest cooling treatment (0.01 °C min−1) results in a large increase in cis-16:1(n-7) and significant reductions in the saturated phospholipid fatty acids 16:0, 18:0 and the unsaturated 16:1(n-9) and 18:2(n-6) fatty acids. These changes cause a slight decrease in the average length of the phospholipid fatty acids and an increase in the overall ratio of unsaturated vs. saturated fatty acids. These findings demonstrate that the rate of cooling is important for both the reorganization of membrane lipids, and for the degree of acquired cold tolerance during rapid cold hardening, and they suggest an important role for rapid cold hardening during diurnal rather than seasonal temperature changes.

Nutritional value of floral nectar sources for flight in the parasitoid wasp, Cotesia glomerata

Abstract: . This study investigates the feeding of the parasitoid Cotesia glomerata on the floral nectar of Anethum graveolens and Origanum vulgare and evaluates the nutritional value of these food sources for increasing flight capacity. A significantly higher proportion of females are observed feeding on A. graveolens immediately after being released onto the floral nectar plants compared with those of the group released onto O. vulgare, although female wasps from both groups spent a similar period of time feeding on both nectar sources and there is no significant difference in their body weight increase. Laboratory tests on computer-linked flight mills demonstrate that adult feeding significantly influences flight capacity, as defined by the number of flights, the longest single flight and the total distance flown during a given period of time, in female wasps but not in males, albeit the extent of influence varying with the type of food sources. After ad libitum feeding on the floral nectar of A. graveolens, female wasps perform flight activity as well as those feeding on honey, which is superior to those feeding on sucrose, in all the measured parameters. Feeding on the floral nectar of O. vulgare has a similar effect to feeding on the extrafloral nectar of Vicia faba and significantly increases the total distance flown but not the number of flights or the longest single flight. Feeding on sucrose does not increase flight capacity in the parasitoids beyond those having access to water only. The findings of this study suggest that judicious selection of floral nectar plants and habitat manipulation might play a key role in the biological control of pest insects.

Facultative ‘secondary’ bacterial symbionts and the nutrition of the pea aphid, Acyrthosiphon pisum

Abstract: Facultative ‘secondary’ bacterial symbionts influence various traits of aphids, including plant utilization patterns and resistance to parasitoids The present study is designed to test the hypothesis that these multiple effects are underlain by symbiont-mediated changes to the aphid requirement for the dominant dietary nutrients, sucrose and amino acids The performance of pea aphids (Acyrthosiphon pisum) on chemically defined diets of systematically altered sucrose and amino acid content varies among eight parthenogenetic clones, with a pattern that does not match the aphid complements of secondary symbionts, Hamiltonella defensa, Regiella insecticola and Serratia symbiotica Aphid performance is reduced, increased and unaffected by elimination of S symbiotica, R insecticola and H defensa, respectively, but with no significant effect on the range of diets on which aphids performed well It is concluded that the impact of secondary symbionts on aphid traits is most unlikely to have a purely nutritional basis

Oogenesis in the date stone beetle, Coccotrypes dactyliperda, depends on symbiotic bacteria

Abstract: . It has been suggested that sex ratio distorting symbionts are involved in the sex determination and female-biased sex ratios observed in strongly inbred scolytid beetles. Coccotrypes dactyliperda (Coleoptera: Scolytinae) is a species in which mother-son- and sib-mating occur inside the date seeds it inhabits, and the sex ratios produced are highly skewed toward females. In the present study, polymerase chain reaction (PCR) techniques and antibiotic treatments are applied to determine the possible role of Bacteria in this system. PCR with primers specifically designed to target the 16S rDNA gene in all Bacteria reveals the presence of Wolbachia and Rickettsia in control beetles, but not in antibiotic-treated individuals. Virgin females fed with antibiotics lay no eggs, and no sign of oogenesis is detected compared with all-male progeny of virgin control females. Mated females fed with antibiotics lay significantly fewer eggs than control females, with a strong effect of female age at the time of antibiotic feeding on the number of eggs laid. The study suggests that symbiotic bacteria are not involved in female-biased sex ratios but are required for oogenesis in C. dactyliperda. The specific role each of the bacteria (Wolbachia and Rickettsia) plays in the oogenesis remains to be determined.

Effect of long‐term and rapid cold hardening on the cold torpor temperature of an aphid

Abstract: The effect of long-term (seasonal) acclimation and rapid cold hardening is investigated on the cold torpor temperature (CTmin) of adult grain aphids, Sitobion avenae, reared at 20 or 10 °C for more than 6 months before experimentation. Rapid cold hardening is induced by exposing aphids reared at 20 to 0 °C for 3 h and aphids reared at 10 to 0 °C for 30 min (acclimation regimes previously found to induce maximum rapid cold hardening). The effect of cooling aphids from the same rearing regimes from 10 to −10 °C at 1, 0.5 and 0.1 °C min−1 is also investigated. In the 20 °C acclimated population, rapid cold hardening and cooling at 0.1 °C min−1 both produce a significant decrease in CTmin from 1.5 ± 0.3 to –0.9 ± 0.3 and –1.3 ± 0.3 °C, respectively. Rapid cold hardening also results in a significant reduction in CTmin of the population reared at 10 °C from 0.8 ± 0.1 to –0.9 ± 0.2 °C. However, none of the cooling regimes tested reduces the CTmin of the winter-acclimated (10 °C) population. The present study demonstrates that rapid cold-hardening induced during the cooling phase of natural diurnal temperature cycles could lower the movement threshold of S. avenae, allowing insects to move and continue feeding at lower temperatures than would otherwise be possible.

The roles of olfaction and vision in host‐plant finding by the diamondback moth, Plutella xylostella

Abstract: The relative roles of olfaction and vision in the crepuscular host-finding process of a major lepidopteran pest of cruciferous crops, the diamondback moth Plutella xylostella are investigated in a series of laboratory and semi-field experiments. Flying female moths use volatile plant chemical cues to locate and to promote landing on their host, even in complex mixed-crop environments in large cages. Multiple regression analysis shows that both the plant position (front, middle or back rows) and the type of plant (host plant, nonhost plant) are needed to explain the distribution of insects in such a mixed-crop situation. This strong plant position effect indicates that, when host plants are present in a mixture, foraging P. xylostella are more likely to alight on the first row of the plants. The findings are discussed with regard to current theories of host-plant location by phytophagous insects and the possible implications for integrated pest management.

Host recognition by a polyphagous lepidopteran (Helicoverpa armigera): primary host plants, host produced volatiles and neurosensory stimulation

Abstract: An important question in the host-finding behaviour of a polyphagous insect is whether the insect recognizes a suite or template of chemicals that are common to many plants? To answer this question, headspace volatiles of a subset of commonly used host plants (pigeon pea, tobacco, cotton and bean) and nonhost plants (lantana and oleander) of Helicoverpa armigera Hubner (Lepidoptera: Noctuidae) are screened by gas chromatography (GC) linked to a mated female H. armigera electroantennograph (EAG). In the present study, pigeon pea is postulated to be a primary host plant of the insect, for comparison of the EAG responses across the test plants. EAG responses for pigeon pea volatiles are also compared between females of different physiological status (virgin and mated females) and the sexes. Eight electrophysiologically active compounds in pigeon pea headspace are identified in relatively high concentrations using GC linked to mass spectrometry (GC-MS). These comprised three green leaf volatiles [(2E)-hexenal, (3Z)-hexenylacetate and (3Z)-hexenyl-2-methylbutyrate] and five monoterpenes (α-pinene, β-myrcene, limonene, E-β-ocimene and linalool). Other tested host plants have a smaller subset of these electrophysiologically active compounds and even the nonhost plants contain some of these compounds, all at relatively lower concentrations than pigeon pea. The physiological status or sex of the moths has no effect on the responses for these identified compounds. The present study demonstrates how some host plants can be primary targets for moths that are searching for hosts whereas the other host plants are incidental or secondary targets.

Effects of diapause duration on future reproduction in the cabbage beetle, Colaphellus bowringi: positive or negative?

Abstract: Cabbage beetles, Colaphellus bowringi, undergoing an imaginal summer and winter diapause in the soil, show a great difference in diapause duration (from several months to more than 3 years) under natural conditions The effects of diapause duration on future reproduction in the beetle are investigated at 25 °C with an LD 14 : 10 h photoperiod and under natural conditions The fecundity of postdiapause adults with a short diapause of 5 months and nondiapause adults is similar, showing that a short diapause has no affect on reproduction, whereas the longevity of postdiapause adults with a short diapause of 5 months is significantly shorter than nondiapause adults, showing that a short diapause has a negative affect on longevity The mean total egg production per female and longevities of postdiapause adults with long diapause periods of 16, 22, 29 and 34 months are similar to nondiapause adults, but the mean daily egg production per female is significantly higher than nondiapause adults, showing that extended diapause has a positive effect on postdiapause reproduction The offspring of postdiapause parents require a relatively shorter time for egg development compared with the offspring of nondiapause parents, showing that diapause has a positive effect on their offspring's performance However, there are no significant differences among offspring performance in terms of survival, adult longevity, mean egg production per female and mean daily egg production per female

Additive effect of teratocyte and calyx fluid from Cotesia plutellae on immunosuppression of Plutella xylostella

Abstract: Teratocytes are cells that originate from the extra-embryonic tissues of some hymenopteran parasitoids, typically dissociate upon hatching, and develop in the host haemolymph. They are considered to be involved in parasitoid larval nutrient uptake, host immunosuppression and/or repression of competing parasitoid development. Teratocytes of the parasitoid, Cotesia plutellae (Kurdjumov) (Hymenoptera: Braconidae) are found in its natural host, Plutella xylostella (Linnaeus) (Lepidoptera: Yponomeutidae) and can be cultured in vitro. The present study demonstrates that teratocytes of C. plutellae possess a significantly depressive effect on host cellular immunity. When the hosts are preinjected with 200 cultured teratocytes (corresponding to the normal number of teratocytes released during wasp hatching), haemocyte nodulation is inhibited by approximately 40%, with younger teratocytes being more potent than older ones. Similarly, the medium in which teratocytes are cultured has similar immunosuppressive properties. In comparison, calyx fluid extracted from the C. plutellae ovary also has an immunosuppressive effect on P. xylostella. These two maternal (calyx fluid) and embryonic (teratocytes) factors are additive and result in a reduced level of nodule formation equivalent to that induced by natural parasitization. However, the immunosuppression of the parasitized P. xylostella does not appear to be due to inhibition of phospholipase A2, an immune mediator, because injection of arachidonic acid failed to restore haemocyte nodulation capability.

Chemical information from the fungus Amylostereum areolatum and host-foraging behaviour in the parasitoid Ibalia leucospoides

Abstract: Parasitoids locate hosts using reliable and predictable cues such as smells derived from host plants or from the hosts themselves. For host species that live with mutualistic organisms, such as several wood boring insects, cues derived from the symbionts are likely to be exploited by specific parasitoids. Through a set of bi- oassays, the behaviour of the parasitoid Ibalia leucospoides Hochenwarth (Hymenoptera: Ibaliidae) is studied in response to the fungus Amylostereum areola- tum Boidin (Basidiomycotina: Corticiaceae), a symbiont of its host, the wood wasp Sirex noctilio Fabricius (Hymenoptera: Siricidae). The results show that parasitoids are attracted to the fungus when growing naturally within pine logs, and also when growing on an artificial medium. Fungal volatiles also elicit increased parasitoid activity and may provide information on relative densities of hosts available for parasitization. It is speculated that the the chemical information derived from the host fungal symbiont comprises reliable and detectable host-locating cues used by parasitoids to search for concealed hosts.

Sperm ejection as a possible cryptic female choice mechanism in Odonata (Insecta)

Abstract: . The few odonate studies of sperm use suggest that females spend apparently more sperm than appears necessary during oviposition (sometimes females may have their sperm stores reduced to 50% after a single oviposition episode). Furthermore, some studies document that females eject sperm during and after copulation. This raises the question of whether sperm reduction may be interpreted as a cryptic female choice mechanism. Using two zygopterans, Ischnura denticollis Burmeister and Enallagma praevarum Hagen, and one anisopteran, Pantala flavescens Fabricius, it is shown that females mate more than once, show a marked reduction in stored sperm, and that this is by ejection of sperm before to oviposition. The extent of sperm reduction is inversely related to the number of eggs laid. When mated to the same male, females show similar reductions in sperm stores and egg load and only rarely does the vaginal duct contain sperm. This suggests that marked sperm reduction is common in this insect order and is not explained by an excess of sperm obstructing the egg passage. It is suggested that female's sperm shortage is better explained as a cryptic female choice mechanism aimed at favouring the sperm of some males. This study provides exciting research avenues for future studies of female choice in an animal taxa whose sexual biology is otherwise regarded as controlled by males.

Rapid cold-hardening in a Karoo beetle, Afrinus sp.

Abstract: . In the insect rapid cold-hardening response, survival at subzero temperatures is greatly improved by a brief pre-exposure at a milder temperature. It is predicted that insects with minimal cold tolerance capabilities living in variable environments should use rapid cold-hardening to survive sudden cold snaps. This is tested in Afrinus sp., a beetle that lives in an exposed habitat on rock outcrops in the Karoo Desert, South Africa, where microclimate temperatures drop infrequently to below freezing. Afrinus sp. shows a significant rapid cold-hardening response: survival of a 2-h exposure to −6.5 °C is much improved after pre-exposure to −2 °C, to 0 °C with a 2-h return to the rearing temperature, and to 40 °C, but not after pre-exposure to 0 °C. Little is known about the mechanism of the rapid cold-hardening response, although the data suggest that rapid cold-hardening may be mediated via several different mechanisms.

Comparing the effects of five naturally occurring monosaccharide and oligosaccharide sugars on longevity and carbohydrate nutrient levels of a parasitic phorid fly, Pseudacteon tricuspis

Abstract: . The longevity and nutrient levels of Pseudacteon tricuspis provided with 1 m solutions of five naturally occurring sugars, fructose, glucose, sucrose, trehalose and melezitose, are compared. All but melezitose, result in significant increases in the longevity of P. tricuspis in comparison with sugar-starved flies (flies provided with water only). Sugar-starved female and male P. tricuspis have an average longevity of 3.3 and 4.1 days, respectively. Provision of free water in addition to sugar solution is necessary for optimum longevity by female and male flies. Longevity is increased by 2.4–2.6-fold by the two monosaccharides, fructose and glucose, and by 2.6–2.8-fold by the disaccharides, sucrose and trehalose. Phorid flies provided with the trisaccharide sugar, melezitose, had a marginal increase in lifespan (approximately 1 day), but this is not significantly different from the longevity of sugar-starved flies. Significantly greater levels of total sugars are detected in P. tricuspis fed the disaccharide sugars (sucrose, trehalose) or the monosaccharide sugars (fructose, glucose), compared with flies provided with melezitose (trisaccharide), or to sugar-starved flies. Fructose is not detected in sugar-starved flies, or in flies fed glucose or trehalose. However, high levels of fructose are detected in flies fed sucrose or fructose, whereas levels of fructose in melezitose-fed flies are intermediate. In general, significantly greater glycogen levels are detected in P. tricuspis fed sucrose, glucose, trehalose or fructose, compared with melezitose-fed or sugar-starved flies. Levels of total sugars and glycogen in sugar-fed flies are positively correlated with wing length, possibly indicating a higher accumulation of storage sugars by larger flies. These results are discussed in relation to the nutritional ecology of the phorid fly.

Oviposition by Lobesia botrana is stimulated by sugars detected by contact chemoreceptors

Abstract: . The influence of glucose, fructose and sucrose on oviposition site selection by Lobesia botrana is studied by combining behavioural and electrophysiological experiments. Oviposition choice assays, using surrogate grapes treated with grape berry surface extracts of Vitis vinifera cv. Merlot at different development stages, show that L. botrana females are most stimulated by extracts of mature berries containing the highest concentrations of glucose and fructose. Choice assays reveal that the oviposition response to these sugars is dose-dependant (with a threshold of the applied solution = 10 mm and a maximum stimulation at 1 m) and that females are more sensitive to fructose than to glucose. Tarsal contact-chemoreceptor sensilla are unresponsive to stimulation with sugars but the ovipositor sensilla contain at least one neurone most sensitive to fructose and sucrose with a threshold of approximately 0.5 mm. Corresponding to the behavioural data, glucose is significantly less stimulatory to sensilla than fructose or sucrose. It is argued that fructose may be of special importance for herbivorous insects exploiting fruit as an oviposition site.

Size variation and mating success in the stag beetle, Lucanus cervus

Abstract: The stag beetle, Lucanus cervus, is Britain’s largest beetle, with a patchy distribution in southern England. The literature suggests that it displays exceptional size variation, particularly in the males, but no analysis of size inequality has ever been conducted. In the present study, stag beetle adults are measured and allometric relationships derived between various parameters and total body length. Most of the specimens found each year are fragments and head width can be used as a good predictor of total body length in each sex. Body size differs between years and between localities and male beetles show a greater degree of size inequality than females. However, L. cervus does not show greater inequality in size than many other beetle species and populations of males are composed of a relatively large number of small individuals. These males are not at a disadvantage in mating because it is the ratio of male : female size that determines mating success. Very large males are less successful in mating and it is suggested that lack of mating success may act as an additional constraint on mandible size in this species. Size variation is most likely caused by variation in larval food resources, coupled with variation in local climatic conditions.

Thermal conditioning of fifth‐instar Cydia pomonella (Lepidoptera: Tortricidae) affects HSP70 accumulation and insect mortality

Abstract: Levels of HSP70 protein of fifth-instar codling moth [Cydia pomonella (L.) (Lepidoptera: Tortricidae)] are determined after conditioning at 35 °C for different times and also after recovery at 22 °C. Protein samples from larvae conditioned for different times are separated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis electrophoresis. Sub-lethal thermal conditioning at 35 °C for 40 min, 2, 6 and 18 h induces new protein bands in the extracts from treated codling moth larvae. Immunodetection with an antibody to a heat-inducible HSP70 indicates a stronger reaction after 35 °C for 2, 6 and 18 h than after 35 °C for 40 min or control and, during the recovery period at 22 °C, the level of heat shock protein decreases. Conditioning of fifth-instar codling moths at 35 °C also induces thermotolerance in the insects and necessitates longer times at a lethal temperature to ensure mortality. Thermotolerance is correlated with the accumulation of heat inducible HSP70 protein.

Antennal olfactory sensitivity in response to task‐related odours of three castes of the ant Atta mexicana (hymenoptera: formicidae)

Abstract: The relationship between scent composition and antennal sensitivity in different castes of Atta mexicana is investigated under laboratory conditions. Extracts of dead ants are analysed by gas chromatography-mass spectrometry to identify the compounds presumably responsible for the specific undertaking behaviour. Oleic acid is identified as one compound that triggers undertaking behaviour. To determine differences in odour reception between workers of different castes (i.e. foragers, undertakers and soldiers), further antennal sensitivity to task-related odours is tested using electroantennographic techniques. Soldiers are the most specialized caste because of their low response to all odours, except odourants related to alarm pheromones. The behavioural specialization of soldiers and their reduced behavioural repertoire are discussed.

Olfactory cues and nest recognition in the solitary bee Osmia lignaria

Abstract: . The use of olfactory cues for nest recognition by the solitary bee Osmia lignaria is studied in a greenhouse environment. Glass tubes are provided as nesting cavities to allow the in-nest behaviour of bees to be observed. In addition, each glass tube is cut into three sections for experimental manipulation and for subsequent chemical analysis. Nesting females drag their abdomen along the tube before exiting, spiral inside the tube, and sometimes deposit fluid droplets from the tip of the abdomen. For the manipulation, the outer section, the middle section, or both sections are removed and replaced with similar clean glass tube sections, and the behaviour exhibited by test females is recorded upon arrival in front of the nesting site and inside the nesting tubes. The resulting hesitation behaviour displayed by females after treatments appears to indicate the loss of some olfactory cues used for nest recognition inside the entire nest. Chemical analysis of the depositions inside the nesting tube, as well as analysis of the cuticular lipids of the nesting bees, reveals the presence of free fatty acids, hydrocarbons and wax esters.

Do parasitoid preferences for different host species match virulence

Abstract: . Leptopilina boulardi is a parasitoid wasp specialist of Drosophila larvae of the melanogaster subgroup. In Mediterranean areas, natural populations are highly virulent against their main host Drosophila melanogaster. In Congo, populations are less virulent against D. melanogaster but are able to develop successfully inside the tropical African species Drosophila yakuba. Host preferences are compared between two laboratory isofemale lines of L. boulardi, obtained from populations of Congo and Tunisia, respectively, and differing in virulence levels against D. melanogaster and D. yakuba. Host selection is studied by offering female parasitoids a choice between larvae of the two host species. In agreement with optimal foraging models, the line highly virulent against D. melanogaster shows a clear preference for this host species. The other line, less virulent against D. melanogaster but more virulent against D. yakuba, prefers to oviposit on D. yakuba. Such preferences can be observed after a period of host-patch exploitation only, suggesting that experience plays an important role in the host-selection process. These results evidence the existence of intraspecific variability in preference between two host species in L. boulardi, a major requisite in theoretical models of parasite specialization by the host. They also sustain the hypothesis that intraspecific variation in parasitoid preferences between host species might mirror intraspecific variation in virulence.

Electrophysiological responses of the antennal campaniform sensilla to rapid changes of temperature in the ground beetles Pterostichus oblongopunctatus and Poecilus cupreus (Tribe Pterostichini) with different ecological preferences

Abstract: Cold cells innervating antennal campaniform sensilla of the ground beetles Pterostichus oblongopunctatus (Fabricius, 1787) and Poecilus cupreus (Linnaeus, 1758) belonging to the tribe Pterostichini fire at a stationary rate of 22-23 imp s � 1 at 23 � C. In P. oblongopunctatus, there is a strong negative corre- lation between the stationary firing rate of the cold cell and temperature. By contrast, no relationship between the firing rate and temperature is observed in P. cupreus. Mean peak frequencies, reaching up to nearly 500 Hz, and first- second firing rates, reaching up to 140 imp s � 1 , are observed at the beginning of the phasic-tonic response to rapid cooling of the cold cells of P. cupreus, which are significantly higher than those for P. oblongopunctatus. However, firing rates of the cold cells of the two ground beetles studied do not differ 3 s later, during the tonic stabilization period of the response. The length of the long interspike period, lasting up to several seconds, at the beginning of rapid warming, is a positive function of the extent of change in temperature, and is longer in P. oblongopunctatus than in P. cupreus. These differences in the responses of the cold cells are related to the ecological preferences of the two ground beetles.

Thermal response in adult codling moth

Abstract: . The thermoregulation behaviour of the adult codling moth, Cydia pomonella, is investigated in the laboratory using temperature gradient experiments. Unmated males and females are tested at dawn when moths typically move to resting sites. Mated females are tested during oviposition over a complete diurnal cycle. Temperature strongly affects microhabitat selection in adult moths. Unmated males and females prefer to rest at the low-temperature ends of temperature gradients between 15 and 32 °C. Relative humidity does not influence the thermal response in unmated females, whereas males show a less distinct temperature selection under high humidity. By contrast to unmated moths, ovipositing females prove to be highly thermophilous (i.e. they deposit the highest proportions of their eggs in the zones of highest temperatures of gradients between 15 and 36 °C). This striking discrepancy in thermal response of females between their premating and oviposition period is likely to reflect an adaptation to different selection pressures from the thermal environment. Unmated moths may benefit from low temperatures by a longer lifespan and crypsis within the tree canopy, whereas the choice of warmer oviposition sites by mated females will favour a faster development of eggs.

Rates of metabolism in diapausing and reproductively active tropical butterflies, Euploea core and Euploea sylvester (Lepidoptera: Nymphalidae)

Abstract: Although the ecology of diapause has been widely studied in the field, the underlying physiological responses occurring in tropical diapausing insects remain virtually unexplored. This is especially the case with rates of respiration in diapausing tropical insect species. The present study compares rates of metabolism, as assessed by measurement of carbon dioxide production, between two species of diapausing and reproductively active tropical butterflies, Euploea core (W.S Macleay) and Euploea sylvester (Fabricius), independent of temperature. Measurement of metabolism over a day-time/night-time regime confirms that these tropical butterflies display a diurnal rhythm in accordance with many other tropical and temperate insect species, regardless of developmental state. In addition, diapausing Euploea butterflies display rates of carbon dioxide production only 28% lower than those of reproductively active butterflies, and can terminate diapause within days of receiving the correct cues. Maintaining a similar metabolic rate throughout diapause, as well as a rapid termination of diapause, would enable these tropical butterflies to respond immediately to larval host plant resources, without the disadvantage of missing optimum conditions, allowing the species to maximize their reproductive potential.

Effects of temperature of adults and eggs on the induction of embryonic diapause in the band-legged ground cricket, Dianemobius nigrofasciatus

Abstract: Eggs laid by adult female Dianemobius nigrofasciatus, reared under long-day (LD 16 : 8 h, 25 °C) or short-day (LD 12 : 12 h, 25 °C) conditions from the nymphal stage, are kept at several constant temperatures. At 22.5–30.0 °C, eggs laid by long-day adults show lower incidences of diapause than those laid by short-day adults. In both eggs laid by adults under long-day conditions and those under short-day conditions, the higher the temperature at which the eggs are kept, the lower the incidence of diapause. When eggs of long-day adults are exposed to a low-temperature pulse (10 °C, 24 h) on the day of deposition (day 0), the incidence of diapause increases. The low-temperature pulse on day 1 does not increase the incidence of diapause. By contrast, when the eggs of short-day adults are exposed to a high-temperature pulse (35 °C, 24 h) on day 0 or day 1, the incidence of diapause decreases. The temperature pulses on day 0 are more effective at diapause prevention. Staining of diapause eggs by the Feulgen–Rossenbeck method shows that the eggs enter diapause at the blastoderm stage, which is on day 1 or day 2 at 25 °C. The exposure of adults to long days and higher temperatures prevents the eggs from entering diapause. In D. nigrofasciatus, embryonic diapause is controlled by maternal effects, adult photoperiod and temperature, and egg temperature before or at diapause.

Transmission of stridulatory signals of the burrower bugs, Scaptocoris castanea and Scaptocoris carvalhoi (Heteroptera: Cydnidae) through the soil and soybean

Abstract: Males and females of the burrower bug species Scaptocoris castanea Perty and Scaptocoris carvalhoi Becker emit stridulatory signals when on the roots of soybean. The substrate-borne components of the signal can be recorded on the plant but not on the surrounding soil surface. The stridulatory apparatus is composed of the tergal plectrum (lima) and the stridulitrum (stridulatory vein) on the underside of the hind wings. The male plectrum has one ridge and the female lima has 13 ridges. Stridulitra of different species differ in the length and in the number of teeth. Rubbing of plectrum (lima) ridges over the stridulitrum in one or both directions produces pulse trains. The velocity of signals that are recorded less than 0.5 cm from the bug is below 0.013 mm s−1 on the soil and below 0.066 mm s−1 on the leaf surface. Broadband spectra have a dominant frequency of less than 1 kHz and subdominant peaks extending up to 7 kHz. The dominant frequency of the stridulatory signal transmitted through a plant decreases together with the proportion of its higher frequency spectral components. Signals are attenuated for 3–9 dB cm−1 when transmitted through the soil or soybean leaf and for approximately 1 dB cm−1 when transmitted through soybean stem.

High water-loss rates and rapid dehydration in the burying beetle, Nicrophorus marginatus

Abstract: During the summer months, there is a high mortality of burying beetle (Coleoptera: Silphidae) species in pitfall traps containing dry soil. The present study investigated the possibility that the burying beetle Nicrophorus marginatus is highly susceptible to death from desiccation. In the laboratory, adult beetles lose 1-5% body mass per hour in low humidity conditions (25-30% relative humid- ity), depending on temperature. This rate of water-loss results in a 50% mortality within 7-16 h at temperatures between 16 and 28 � C. Nicrophorus marginatus produces oral and anal defensive secretions when disturbed but these secretions do not significantly contribute to the high rate of water loss. Beetles readily drink and thus beetles with access to water or in high humidity conditions suffer near zero mortality. For comparison, the similarly sized mesic bess beetle (Coleoptera: Passalidae), Odontotaenius disjunctus, and a large nocturnal tiger beetle (Coleoptera: Cicindelidae), Amblychila cylindriformis, are exposed to dehydrating conditions. Nicrophorus marginatus have higher rates of water-loss (by 26% and 79%, respectively). It is predicted that the diurnal N. marginatus uses behavioural mechanisms to avoid lethal water loss. In the field, N. marginatus displays a strong bimodal activity pattern, avoiding the hottest hours of the day. The significance of these findings is that N. marginatus defies normal predictions of association between water-loss rates and habitat type, and has extended its range into apparently unfavourable habitats despite high water-loss rates. In addition, the results suggest that researchers should provide moisture when studying bury- ing beetles, including the endangered American burying beetle (Nicrophorus americanus).

Microclimatic factors influencing refugium suitability for Rhodnius prolixus

Abstract: Rehydration in the triatomine bug Rhodnius prolixus (Stal) is dependent on the blood meal, and water balance regulation is crucial for survival of starving bugs In an experimental arena with zones at different climatic conditions, starved R prolixus nymphs prefer a cooler and more humid zone, stopping there more often and for longer periods This is probably a behavioural adaptation to limit water loss and reduce metabolic rate In the Venezuelan State of Portuguesa, temperature and humidity were monitored in three kinds of potential refugia during the dry season: (i) in a palm roof; (ii) in a crack of the wall of a house; and (iii) in a palm tree crown Fluctuations in temperature and saturation deficit are not very different inside and outside the palm roof except during a few hours of the day when the sun is at its zenith In the crack of the wall, the diurnal temperature range is reduced to 65 � C compared with 124 � C outside, and the saturation deficit varies by only 76 hPa compared with 286 hPa outside In the palm tree crown, the daily temperature range is only 42 � C compared with 138 � C outside, and the saturation deficit is permanently < 5 hPa The micro- climatic conditions in the palm tree crown would appear to be ideal for starving R prolixus, but this kind of refugium generally harbours low densities of bugs, probably related to a combination of predation, pathogens and lower mean temperature within the crown Such biotic and abiotic constraints play a lesser role in the less ideal palm roof and wall crack refugia where bugs can proliferate as long as hosts are readily available nearby

Respiration by mangrove ants Camponotus anderseni during nest submersion associated with tidal inundation in Northern Australia

Abstract: The ant Camponotus anderseni lives exclusively in twigs of the mangrove tree Sonneratia alba, which forms the fringe at the wettest part of the mangrove zone. During inundation, which can last up to 3 h, the entrance hole to the nest cavity is blocked with a soldier's head that effectively prevents flooding, but simultaneously blocks gas exchange with the surroundings. The ants and brood, together with their mutualistic Coccid, Myzolecanium sp. 1, occupy an average of 23% of the volume of the nest cavities (maximum of 50%). Measurements of CO2 production in the laboratory indicate respiratory rates of 1.90 and 0.41 µL CO2 h−1 mg−1 live mass at 25 °C for workers and larvae, respectively. Measurements of sealed natural nests show that mean respiratory rates decrease to 18.9% and 1.8% of the normoxic rate at CO2 concentrations of 10% and 25%, respectively. In artificial nests where the initial CO2 is elevated, the respiratory rates after 1 h are reduced to 48% and 2.3% of the normoxic rate when exposed to CO2 concentrations of 10% and 25%, respectively. Air samples from natural nests in the field taken more than 12 h after inundation have mean CO2 concentrations of up to 4–5%, which means that the CO2 concentration in the parts farthest from the entrance must be much higher. In sealed nests in the laboratory, the O2 concentration after 1 h decreases by 6.8% and, in the same period, the CO2 concentration increases by 12.1%, which suggests that the ants have partly switched to anaerobic respiration. The rapid and extreme depression of the respiratory rates of C. anderseni represents an outstanding physiological adaptation that allows their survival under the extreme conditions of tidal inundation.